Dirhodium(II) tetracarboxamidates derived from chiral methyl 1-acyl-2-oxoimidazolidine-4(S)-carboxylates are highly enantioselective and diastereoselective catalysts for metal carbene transformations of diazoacetates. Four of these catalysts have been prepared by ligand substitution with dirhodium(II) acetate and characterized spectroscopically and by X-ray structural analysis. The simplest member of the series, (2,2-cis)-dirhodium(II) tetrakis[methyl 1-acetyl-2-oxoimidazolidine-4(S)-carboxylate], (2,2-cis)-Rh-2(4S-MACIM)(4), forms monoclinic crystals in space group P2(1) with cell constants of a = 9.959(1) Angstrom, b = 20.100(1) Angstrom, c = 11.678(1) Angstrom, beta = 107.61(1)degrees, V = 2228.1(3) Angstrom(3), and Z = 2. (2,2-cis)-Rh-2(4S-MBOIM)(4), whose 1-acyl group is phenyl, forms tetragonal crystals in space group P4(1)2(1)2 with cell constants of a = 18.352(1) Angstrom, c = 17.067(1) Angstrom, V = 5748.1(6) Angstrom(3), and Z = 4. The most enantioselective catalyst in many metal carbene transformations is the one with 3-phenylpropanoyl at the 1-position, (2,2-cis)-Rh-2(4S-MPPIM)(4); crystals are monoclinic in space group P2(1) with cell constants of a = 11.589(1) Angstrom, b = 12.225(1) Angstrom, c = 21.802(2) Angstrom, beta = 94.429(8)degrees, V = 3079.6(5) Angstrom(3), and Z = 2.